A man and a woman have been arrested on suspicion of murder after five children aged 10 or under died in a house fire early on Friday.

A major investigation is taking place into the fierce blaze that broke out at a property in Allenton, Derby, shortly before 4am. Flames and smoke rapidly spread through the house, thwarting rescue attempts by the children's parents, neighbours and 30 firefighters.

The children were named by police as Jade Philpott, 10, John Philpott, nine, Jack Philpott, seven, Jessie Philpott, six, and Jayden Philpott, five. A sixth child, Duwayne, 13, is seriously ill in a hospital in Birmingham, and is receiving specialist treatment.

They were asleep upstairs when the fire broke out, and their father made "valiant efforts" to save them, said Derbyshire police's assistant chief constable, Steve Cotterill. The father, who has been named locally as Mick Philpott, escaped with minor injuries because he and his wife were asleep downstairs, police said.

It is believed the 28-year-old woman under arrest knows the family, who had previously lived in an unconventional arrangement in which Philpott shared the home with his wife and girlfriend and their 10 children. According to friends, until recently, the couple and their children shared the house with Philpott's ex-girlfriend, but the relationship ended acrimoniously.

There have been allegations on social networking sites that the family was subject to threats, but police refused to comment.

On Friday night, a 38-year-old man from Derby was also under arrest.

Neighbours spoke of being woken by noise early on Friday morning as other residents shouted for help and tried to get into the burning house. Joe Peel, who lives nearby, said he was woken by his dog. "I got up, I looked outside and it looked really foggy," he said. "I looked across the road and one of the house's doors was just covered in flames... I ran out of the house, screaming to the neighbour to wake him up."

Peel said he could hear his neighbour's voice, but could not get into the house because of the flames and smoke. "Two or three minutes later you could see the flames going up the stairs through the side window. It was absolutely horrible."

Five years ago, the family featured in a tabloid newspaper when Philpott complained that he needed a bigger council house as he had 14 children. Former Tory MP Ann Widdecombe later made a documentary about them.

Neighbour Sam Smith, 30, said: "There had been a lot of negative publicity about him over the years, but no family deserves this. It is an absolute shock. No parent should have to go through losing one child, let alone five. From my experience of Mick, he has always been a pleasant man. He adored his children."

The road, Victory Road, is close to the Rolls-Royce factory and takes its name from the 'winged victory' badge on its cars.

Daniel Walsh, who has known the family for many years, said it was tragic and shocking: "Any parent's worst nightmare. He [Philpott] had many children, as everybody knows, and he loved them all the same. No doubt. It's just a tragic loss."

Derbyshire fire and rescue service chief fire officer Sean Frayne said 30 firefighters were sent to tackle the blaze. Fire service area manager Gavin Tomlinson said the incident was "frustrating, traumatic and tragic" for the family, relatives and firefighters. Police refused to confirm the identity of the family, saying it would be inappropriate and insensitive.

Cotterill told a press conference that detectives were keeping "an open mind" about the cause of the fire. He confirmed that a woman in her late 20s was arrested, but refused to elaborate.

He said their thoughts were with the parents and family of the children for their tragic loss and for the community "who would, of course, have known the children as they played." He urged people not to read too much into the arrest of the woman. "It is a matter of a police inquiry, where we have to act very quickly to preserve any evidence which may feature later in an inquiry," he said. Potentially, it was a murder inquiry, he added.

All five children attended St George's Catholic primary school in Littleover, Derby. A statement from the school said: "We extend our deepest sympathies to the family and community at this sad time."

Postmortem examinations will be carried out over the weekend and forensic specialists are examining the house.

Widdecombe, who spent a week living with the then 57-year-old Philpott for the programme Ann Widdecombe Versus the Benefit Culture, said: "Nobody would ever call him a bad father. I'm so sorry, and my thoughts are with the family."